The present invention relates to mechanical refrigeration equipment, and more particularly to a device for measuring and controlling the recovery of refrigerant from a mechanical refrigeration system.
Mechanical refrigeration systems are used in a wide variety of applications. These applications include refrigerators, heat pumps, and air conditioners used both in vehicles and in buildings. The vast majority of mechanical refrigeration systems operate according to similar, well known principles, employing a closed-loop fluid circuit through which refrigerant flows. Fluorocarbon refrigerants are the types of refrigerants used most widely today.
Mechanical refrigeration systems periodically require servicing. This servicing often takes the form of the addition of refrigerant into the system to replace refrigerant which has escaped from the system. Other servicing often takes the form of repairs to, or replacements of components in the system such as compressors, evaporators, filters, dryers, expansion valves and condensers.
Before servicing a mechanical refrigeration system, i.e., repairing or replacing one or more components, or even adding refrigerant, it is often necessary to remove the original refrigerant remaining in the system. Historically and typically, this remaining refrigerant was removed by bleeding off the refrigerant to the atmosphere. In recent years, much concern has arisen about this practice of releasing fluorocarbon-based refrigerants into the atmosphere. The release of such fluorocarbons is believed to deplete the concentration of ozone in the atmosphere. This ozone depletion is believed to adversely affect the environment and human health. Numerous laws have been passed requiring recovery of the refrigerant rather than venting.
To avoid releasing fluorocarbons into the atmosphere, devices have been constructed that are designed to recover the refrigerant from the refrigeration system. One difficulty encountered with the removal of refrigerant is the time required to remove the refrigerant. Although removal time is not that critical when servicing a relatively small volume refrigeration system, such as the air conditioning system in a car, or a room air conditioning system, the time required to remove refrigerant from a large system can be substantial. Examples of larger mechanical refrigeration systems include commercial freezers and refrigerators, and air conditioning systems used in commercial, industrial and office buildings.
Mechanical refrigeration systems typically have a high pressure port and a low pressure port through which refrigerant can be introduced to, or removed from the system. The refrigerant in the area of the system adjacent to the high pressure port of the refrigeration system is typically in liquid form. The refrigerant adjacent to the low pressure port of the refrigeration system is typically in a gaseous state.
Most refrigerant purge systems remove the refrigerant from the refrigeration system by evacuating the refrigerant in a gaseous form from the low pressure port of the refrigeration system. Purging is accomplished by means of a recovery machine. A recovery machine sucks in refrigerant at one port and discharges at another (much like a vacuum). Refrigerant can be recovered in either a gaseous or liquid state. Liquid recovery is much faster than vapor. It has been found that the time required to remove refrigerant from a refrigeration system is decreased substantially if the refrigerant is recovered from the system as liquid refrigerant, by removing refrigerant through the high pressure port of the mechanical refrigeration system.
Several difficulties exist with the removal of liquid refrigerant from a refrigeration system. Because liquid refrigerant is non compressible, some measures must be taken to protect the recovery machine. These measures slow down the recovery process. One difficulty is that a compressor cannot be used to draw liquid refrigerant out of the system directly, by placing the compressor in the conduit between the mechanical refrigeration system and a storage tank. The flow of liquid refrigerant through a compressor will likely damage or destroy the compressor.
Another difficulty is that to remove the liquid refrigerant efficiently, pressure should be maintained on the liquid refrigerant to maintain the liquid refrigerant in a liquid state as it moves from a mechanical refrigeration system into the storage tank. If the liquid refrigerant is allowed to expand into its gaseous form, much of the time efficiencies gained by removal of the refrigerant as liquid refrigerant is lost.
One method which has been developed to take advantage of the speed of removal in the liquid state and the ease on equipment of removal in the gaseous state, is the so-called "Push/Pull" method. The Push/Pull method is accomplished as follows. The recovery machine is connected so that it draws vapor off the top of a recovery cylinder. The recovery machine then "pushes" the vapor into the low side of the mechanical refrigeration system being recovered. The vapor pressure in the mechanical refrigeration system increases to a point that it exceeds the liquid pressure in the mechanical refrigeration system and "pushes" the liquid out through the high side of the mechanical refrigeration system into the recovery tank liquid port. This process is monitored via a sight glass. When no more liquid is seen, residual vapor recovery to levels set forth by the Federal Government is begun. The hose or conduit connections are re-arranged so that the recovery machine draws, i.e., "pulls", the residual vapor into the recovery tank until the system is basically void of refrigerant. The advantage of the Push/Pull method is an eight fold increase in recovery speed over prior art techniques.
However, there are drawbacks with this method, primarily in the time lost in removing and reconnecting hoses and/or conduits, as well as the risk of venting small amounts of refrigerant to the atmosphere during switch over.
The first step to recovering refrigerant is to connect a test manifold gauge set to the mechanical refrigeration system, i.e., unit being serviced. After a service person has attached the gauge set to the unit and has determined that the refrigerant must be recovered to accomplish repairs, the service person must attach a recovery machine to the unit. In order to recover liquid with the push/pull method, the service person must position and attach hoses in a different configuration than for the initial testing. Then to complete the recovery in a vapor state, the service person must again reposition the hoses.